Catalytic cracking of petroleum oils



Sept 25, 1945. w. ABAILEY, JR

CATALYTIC CRAKING 0F PETROLEUM OILS Filed June 19, 1944 NJIIIIIIIIIIIim.. .cm

LOtPcOwNE UE 006W EHII' Invenl'or: William A.Bnleg Jn Bg his Aorneg; g%

:E200 @Enamel tions taken from the middle Patented Sept. 25, 1945 OFFICECATALYTIC CRACKING OF PETROLEUM OILS William A. Bailey, Jr., Wilmington,

Calif., assignor to Shell Development Company, San Francisco, Calif., acorporation of Delaware Application June 19, 1944, Serial No. 541,051 '1claims. (ci. iss-5o) This invention relates to an improved process forthe production of valuable products from petroleum involving catalyticcracking. More particularly the invention relates to a combina` tion ofprocess steps whereby excellent yields of high quality gasoline may beobtained along with improved yields of other valuable products from thatportion of petroleum oils boiling above gasoline, v l

When petroleum oil is received at the renery the gases and so-calledstraight run gasoline are removed leaving a partly reduced crude. Thereiiner is then faced with the problem of producing the maximum quantityof quality products from this partly reduced crude. One of the mostvaluable products desired is gasoline, and considerable effort andattention has therefore been given to various ways and means forproducing the maximum quantity of gasoline of the best obtainablequality. One of the most important of the available tools at thereilners disposal is catalytic cracking. Due to the large demand forgasoline, catalytic cracking is becoming almost universally used. Evenwith the best means available, however, it is not practical to convertall of this partly reduced crude to gasoline and there is left thereforea considerable volume of by-product materials of lesser value. In thepast the emphasis has been largely on the production of the maximumquantities of gasoline of the best quality and the by-products formed orleft have largely determined the quantity and quality of secondaryproducts such as fuel oil, kerosene, stove oil, asphalt, coke, etc.

The various fractions of the partly reduced crude are considerablydifferent in composition and some are much more amenable to catalyticcracking than others. In general the preferred feed for catalyticcracking units are those fracof the partly reduced crude. Thesefractions are of the nature of light gas oil or stove oil. The lowerboiling components of the nature of heavy gasoline, naphtha andkerosene, are more refractory and are generally used in secondaryproducts or treated by thermal methods, although in a few cases they arecatalytically cracked along with the light gas oil. Also, the bottomfraction, or reduced crude, is not suited for vapor phase catalyticcracking. In practice the gas oil is removed as completely as possibleunder ordinary fractionation conditions to leave a reduced crude whichis suitable for use as fuel oil. In a few cases this reduced crude hasbeen vaporized in a so-called contact vaporizer and the vapors crackedalong with the gas oil. 'Inis is not usually economical however. sinceno fuel oil is produced, and a large amount of coke must be burned inthe contact vaporizers. In ,all of these methods poor quality Diesel oilis produced as a by-product. When handling the petroleum by thesemethods excellent yields of quality gasoline are generally produced, butonly at the expense ofthe quantity and quality of various otherpetroleum products. It is the purpose of this invention to provide amethod whereby the petroleum may be utilized to better advantage byproducing quality gasoline from the more refractory fractions'of thepartly reduced crude without sacricing yield or quality of secondaryproducts.

It has been found that certain refractory frac- -tions of petroleum,such in particular as the lighter naphtha fractions and the very heavyfractions, may be advantageously cracked catalytically if thesefractions are cracked together under suitable conditions, and that by sodoing excellent yields of quality gasoline may be produced withoutsacrifice of quality Diesel fuel or fueloil,

.The process of the invention in ltsbroader aspect comprises separatingthe partly reduced crude by distillation into a light naphtha fraction,a heavy reflux condensate, and a reduced crude, subjecting the reducedcrude to a flash distillation under reduced pressure to produce a heavyflashed distillate and a'heavy residue, catalytically cracking the heavyflashed distillate together with the light naphtha under selectedconditions, separating from the product a light fraction containinggasoline components and a heavy condensate,` and blending the heavycondensate with the heavy residue to replace the `heavy flasheddistillate and produce a saleable fuel oil.

The above general outline of the process of the invention will beamplified and the more important features and modifications will berie--v scribed in more detail in the following description in connectionwith the accompanying drawing in which a specific embodiment of theinvention is set forth for purposes of illustration. In the accompanyingdrawing, which is in the form of a simplified flow diagram,`there isshown by means of diagrammatic gures, not drawn to scale, one suitableassembly of apparatus arranged for operation according to the presentprocess.

The charging stock, when operating according to the present invention isa crude petroleum or/ one from which the gasoline has been substantiaiiyremoved. If a crude petroleum containing gasoline is used, the gasolineis preferably rst removed to leave a partly reduced crude having aninitial boiling point of at least 300 F. The partly reduced crude isthen separated by distillation into a naphtha fraction, a heavy refluxcondensate and a reduced crude.r The cut point between the naphtha andthe reiiux condensate may vary considerably, but is preferably betweenabout 400 F. and 500 F. This separation may be effected in conventionalequipment in a numbcr of ways. In the modification illustrated in theattached drawing the crude petroleum enters via line I and is charged bypump 2 to a stripping column 3 wherein gasoline and naphtha. areseparated. The gasoline and naphtha are removed overhead via. line 4.Part of the condensate is returned as reflux and the remainder is passedto a fractionation column 5 wherein gasoline is separated from thenaphtha.. The gasoline passes overhead via line 6. The napbtha fractionhaving a boiling range of for instance, 320 to 400 F. is removed vialine 1. The bottom product from column 3 is passed through e. suitableheater and then via line 8 to a fractionating column 9. In column 9substantially all of the hydrocarbon components which can be removed atatmospheric pressure without substantial cracking are removed. Thevarious products may be removed in a single stream or may be segregatedinto various fractions as desired. Thus, for example, in the arrangementshown, a heavy naphtha or kerosene fraction is removed via line I0; alight gas oil fraction suitable for use as Diesel fuel is taken offkvialine Ii; and a heavy gas oil fraction suitable for use as Diesel fuel orfor stove oil is taken oif via line I2. The bottom product is a reducedcrude suitable for use as fuel oil.

The reduced crude is passed throughffheating coils in a suitable heaterand then via line I3 to a vacuum fia-sh column I4 wherein it is vacuumdashed under conditions chosen to remove overhead from between about 40%and about r15% of a heavy flashed distillate. One set of typicalconditions isLfor example, a temperature of about 750 F. and 100 mm.absolute pressure. Steam may be injected via line I6 to aid-indecreasing the residence time and prevent cracking. The ashing operationdoes not involve any appreciable amount of cracking. This is indicatedby the average molecular weight of the flashed distillate. Thus, theaverage molecular weight of the asheddistillate when taking 45% overheadis about 280, and the average molecular weight when taking '70% overheadis about 345. Ingeneral a distillate having an average molecular weightin this range is indicated. This flashed distillate, it is seen,represents the heaviest portion of the petroleum that can be vaporizetwith available equipment without substantial cracking. It is dilcult tovaporize, and invariably contains appreciable amounts of nitrogencompounds and other impurities.

The material removed from the bottom of the flash column I4 is a heavyviscous residue. This material is totally unsuited for fuel oil, but produces a readily saleable fuel oil when blended with aromatic reuxcondensate as hereinafter described. n

In a preferred modification of the process of the invention the iiashingoperation is carried out under somewhat more severe conditions to effecta minor amount of cracking. The amount of cracking is adjusted to givebetween about 50% peinture.

and '75% of a flashed distillate having an average molecular weightbetween about 280 and 360. This may be and is preferably effected Withthe formation of not more than 1% gas and not more than 1% of gasoline.The conditions of tempressure and residence time to give this resultcannot be stated with any degree of definiieness due to the interrelatonof these factors and. the diiierences due to the particular petroleumsource and apparatus effects. However, these conditions are adjusted inthe known manner and may be readily arrived at in any particular case.The distillate obtained under such conditions is hereinafter referred toas flash cracked distillate.

The iiashed distillate or flash cracked distillate produced as describedis combined with the refractory light naphtha fraction from Vcolumn 5and the mixture is subjected to suitable catalytic cracking treatment.The catalytic cracking treatment may be effected in any one of thevarious known systems and with any of the proprietary crackingcatalysts. For reasons which will be pointed out below, however, thecatalytic cracking systems employing iinely divided catalysts which`arecontinuously regenerated are particularly suitable for this operation.Very suitable catalysts are, for example, the activated clays such asFiltrol, and the synthetic catalysts such as the composites ofsilica-alumina, boric oxide-alumina, boric oxide-alumina-silica,silicaalumina-zirconia, silica-magnesia, etc.

As in all cracking processes, the conditions in the cracking zone mayvary individually over a considerable'range. The approximate ranges ofthe individual conditions for optimum results are as follows:

Temperature 950--1050 F. Pressure 0-50 p. s. i. g. Weight hourly spacevelocity 0.5-4 lb/hn/lb. Catalyst oil ratio (fiuid system) 10: 1-30zl,Steam 045% oi oil In the system illustrated in the attached flow diagramthe ashed distillate coming from the vacuum flash column via line l5 isblended with the naphtha fraction from column 5 and the mix ture ispassed via line 1 through the coils of a suitable heater l1. Steam maybe added ii desired via line I8. The pre-heated mixture picks upregenerated flnely divided catalyst entering via standpipe I9 and themixture of oil tapers and finely divided catalyst is passed *o acracking reactor 20. 'The ilows oil vapor and catalyst are adjusted inthe known manner to maintain a bed of the catalyst in reactor 20 in aso-called iiuidized state. Catalyst is continuously withdrawn fromcracking reactor 20 -via standpipe 2i. This material is picked up by astream of air or other regeneration gas and c'arriedvia line 22 to afluid c'nzafvst regenerator 23. The spent regeneration leaves theregenerator via line 24. Regenerated catalyst is removed from thevregenerator via standpipe I9. The oil vapors leave the reactor via line25 and pass to a fractionator 2d, wherein the gasoline and gas areseparated from the heavier cracked and uncracked material. The gasolineand gas are removed overhead via line 2t. The gas which is separated andremoved via line 28 may be sent to a suitable adsorption plant. Part ofthe gasoline is returned to the column 2E for reflux and the remainderis withdrawn via line 29.

A heavy highly aromatic condensate is removed via line 30 and 9, heavyresidue is removed via line 3i. This heavy residue contains a smallamount of catalyst and may be advantageously recycled back to thecrackingr reactor via lines 3| and 1. The condensate consists largely ofhighly refractory aromatic hydrocarbons produced in the cracking zone.This material is passed to a mixing tank 32 wherein it is blended withthe hot vacuum ilashed residue, coming from the vacuum flash column i4via. line 33. A portion of this material may be recycled via line 311 tofractionator 26 to serve as reflux. In View of the highly aromaticnature of the condensate it blends well with the very heavy vacuumflashed residue to produce a stable and superior fuel oil. Also due toits extreme refractivity and low ratio of Yhydrogen to carbon it is avery poor cracking stock and also a very poor Diesel fuel. On the otherhand, this relatively small volume of material is capable of convertinga relatively large `volume of heavy vacuum flashed residue into asuperior fuel oil. Thus, in general it requires only about 50 parts ofthe aromatic condensate to convert 100 parts of the heavy flashedresidue into a superior 100 second fuel oil. When blended 1:1 the heavyashed residue is converted to a stable second fuel cil meeting the NavySpecial grade specifications.

The relative amounts of the light naphtha and liashed distillateavailable from a given petroleum depends upon the particular petroleum,the boiling range of the naphtha fraction, and the depth of flashing,and may vary considerably. .I n some cases the available refractorynaphtha of say 32o-450 F. boiling range may be more than enough to fornia satisfactory blend with the flashed distillate. In this case theboiling range of the light naphtha may be reduced to say 320- 405" F.,or part of the naphtha may be used for other purposes. Also, certainother heavy residues may be added to the reduced crude to increase theamount of flashed distillate. In'general ratios of :dashed distillate tonaphtha of from about 1:1 to about 10:1 are preferred.

It is to be noted that according to .the prevalent belief in the art,the described blend of ilashed distillate and light naphtha would not beconsidered a desirable feed for catalytic cracking. The light naphtha,it will be noted, contains appreciable quantities, and may even consistessentially, of hydrocarbons which can properly be considered asgasoline components. In fact, the light naphtha could in many'cases alsobe called a heavy straight run gasoline. When cracking gas oill stoveoil, and similar intermediate clistillates, it is known that thepresence of gasoline constituents in the feed is quite hanmful. Theprevalent belief in the art is that such gasoline components should beabsent from all catalytic cracking stocks. In the present process thisharmful effect of gasoline components is not no-` ticed, and as pointedout above, the light naphtha in the present process is distinctlybeneficial in certain respects.

Example A crude petroleum was fractionated as described above to producevarious products suchV Table I Flash dis Naphtha miste Gravity ".fl. P.I 41.9 26.7 Aniline point, FM .5 155 Sulfur, percent by We 19 Pourpoint, "F Molecular weight.

. B. P. Less than 100 F., perccnl by volume The conditions used and theyields of products are shown in Table II.

Table II Run number Flaslicd distillate/naphtha ratio. 1:1 3:1 3:1 3:.1

Reactor conditions Pressure. 11.5. i. g l2 12 l2 12 Temperature, uF1,002 1,000 1. 000 1.002 Space velocity, lh/hr/ lh 0. 99 0. 97 1.00 0.63 Catalyst/oil. weight ratio 25 25 21 23 Catalyst bed density, Ib/lt..5 34. 0 35. 8 36.0 Catalyst holding time. minute .4 2. 5 2. 8 4. lSteam, percent of feed .3 19 19.1 16.7

Regenerate.' conditions Pressure p.s.i.g l2 l2 l2 '12 Temperature, F..1,122 1,124 1.127 1,121 Catalyst bed density, lb/i' t 34. 3 29. 7 33. 232.8 Catalyst holding time, minutes 6. 4 6. 4 7. 2 6.8 Carbon on spentcatalyst, percentm.. 0529 0.37 0. 39 0. 56 Carbon oli regeneratedcatalyst.. percent 0. 03 0. 05 0. 06 0. 10

Yields, percent B. W.

2-217 i 4.0 4.6 6.o :1. omi-201 3.3 2.9 2.1 2. cuasi-288 F 4.1 3.a 4.24. 28B-320 F 2.8 3.9 2.6 2. s20-340 r s i 4.4 5. 4 4. ai0-400 r 15.011.7 10.1 7. 400I 21.9 26.9 27.8 24. coke 0.4 8.2 7.0 12.

The 400 E+ material remaining after removing the gases and gasoline ishighly refractory and highly aromatic. Thirty-four parts of the 400 F.+fractions blended with sixty-six parts of the heavy flashed residue gavea Navy No. 2 grade fuel oil which was superior to the usual fuel oils ofthis viscosity prepared with cracked residues. Fifty-one parts of thearomatic 400 F.+ material blended with forty-nine parts of the flashedresidue produced a superior Navy Special grade fuel oil.

oils.

The operations described in the above to illustrate the invention may bemodified in many par ticulars such as the arrangement and order of thefractionation. steps, types of equipment used, etc., while stillemploying the essential features of separating by fractionaldistillation (l) a naphtha fraction, (2) an intermediate fraction of thenature of gas oil and, (3) a reduced crude, subjecting the reduced crudeto the described treatment to produce a flashed distillate or a flashcracked distillate, subjecting the flashed distillate or flash crackeddistillate together with the naphtha fraction to a catalytic crackingtreatment, separating gasoline and heavy aromatic condensate from theproduct and blending the flashed residue or the flash cracked residuewith the heavy aromatic condensate. However, the cracking operation ispreferably one in which a continuously regenerated finely dividedcatalyst is used. As pointed out above, the naphtha fraction crackedaccording to the present process is quite refractory and requires fairlyhigh crackingl temperatures. When this material is cracked alone it isdifficult to maintain the optimum high cracking temperatures. On theother hand the flash distillates and flash cracked distillatesinvariably contain considerable amounts of impurities such as nitrogencompounds. If these materials are cracked alone, large amounts of carbonare formed and the conversions are low, ap-I parently due to thepoisoning effect of the nitrogen bases. When, however, the naphthafraction and the flashed distillate or flash'cracked distil late areblended and cracked together these dis advantages tend to cancel eachother to a certain extent. Thus, the naphtha tends to reduce theconcentration of nitrogen bases and the flash distillate tends toincrease the carbon production over that of the naphtha alone, thusproviding more heat in the regeneration zone. This heat is largelyconveyed to the reaction zone by the hot regenerated catalyst.Furthermore, the flashed distillates and flash cracked distillates arequite heavy and difficult to vaporiae and maintain entirely in the vaporphase without the use of a large amount of steam. The relatively lightnaphtha acts as a diluent and is very beneficial in this respect also.

The present process, it will be seen, allows the production ofconsiderable yields of excellent Diesel fuel from the virgin naphthawithout impairing the quantity or quality of gasoline produced. Thegasoline is produced largely from the flashed distillate or flashcracked distillate while taking advantage of some gasoline productionfrom the refractory naphtha and at the' same time producing therefrom arefractory aromatic condensate which Iis compatible with ashed residueand flash cracked residue and may be used to convert these residues tosuperior fuel Thus, the process of the present invention allows thepetroleum to be utilized to better advantage without sacrificing yieldor quality of secondary products.

I claim as my invention:

1. In the production of useful products includ.- ing gasoline and fueloil from petroleum, the process comprising separating petroleum bydistillation into a gasoline fraction, a light naphtha fraction boilingbetween about 320 F. and 400 F., a heavy reflux condensate, and areduced crude, subjecting the reduced crude to a flash distillationunder vacuum and under mild cracking conditions to produce a heavyresidue and between and 75% of a heavy ash cracked assesses distillatehaving a molecular weight between about 280 and 300 with the formationof less than 1% gas and less than 1% gasoline, subjecting said heavy ashcracked distillate together with said light naphtha to catalyticcracking, separating the cracked product into a gasoline fraction and asecond heavy reflux condensate and combining said second heavy refluxcondensate with said heavy residue to produce fuel oil.

2. In the lproduction of useful products including gasoline and fuel oilfrom petroleum, the process comprising separating petroleum bydistillation into a gasoline fraction, a light naphtha fraction, a heavyreflux condensate, and a reduced crude, subjecting the reduced crude toa flash distillation under vacuum and under mild cracking conditions toproduce a heavy'residue and between 50% and 75% of a heavy flash crackeddistillate having a molecular weight between about 280 and 300 with theformation of less than 1% gas and less than 1% gasoline, subjecting saidheavy flash cracked distillate together with said light naphtha tocatalytic cracking, separating the cracked product into a gaso linefraction and a second heavy reflux condensate and combining said secondheavy reflui: condensate with said heavy residue to produce fuel oil.

3. In the production of useful products including gasoline and fuel oilfrom petroleum, the process comprising separating petroleum bydistillation'lnto a gasoline fraction, a light naphtha fraction boilingbetween about 320 F. and 400 F., a heavy reflux condensate, and areduced crude, subjecting the reduced crude to a flash distillationunder vacuum to produce a heavy residue and between'about 40% and '75%of a heavy flashed distillate having a molecular weight between about270 and 350, subjecting said heavy flashed distillate together with saidlight naphtha to catalytic cracking, separatingthe cracked product intoa gasoline fraction and a second heavy reflux condensate and combiningsaid second heavy reflux condensate with said heavy residue to producefuel oil.

4. In the production of useful products including gasoline and fuel oilfrom petroleum, the process comprising separating petroleum by dis*tillation into a gasoline fraction, a light naphtha fraction, a heavyreflux condensate, and a reduced crude, subjecting the reduced crude toa flash distillation under vacuum to produce a heavy residue and betweenabout 40% and 75% of a heavy flashed distillate having a molecularweight between about 270 and 350, subjecting said heavy flasheddistillate together with said light naphtha to catalytic cracking,separating the cracked product into a gasoline fraction and a secondheavy reflux condensate and combining said second heavy refluxcondensate with said heavy residue to produce fuel oil.

5. In the production of useful products including gasoline and fuel oilfrom petroleum, the process comprising separating petroleum bydistillation into a gasoline fraction, a light naphtha fraction boilingbetween about 320 F. and 400 F., a heavy reflux condensate, and areduced crude, subjecting the reduced crude to a flash distillationunder vacuum to produce a heavy flashed distillate and a heavy residue,subjecting said heavy flashed distillate together with said lightnaphtha to catalytic cracking, separating the cracked product into agasoline fraction and a second heavy reflux condensate and combininggether with ysaid light naphtha. to catalytic cracking, separating thecracked product into a gasoline fraction and a heavier aromaticcondensate and combining said heavier aromatic condensate with saidheavy flashed residue to produce fuel oil.

7. Process according to claim 6 in. which the catalytic cracking iscarried out with a finely divided catalyst which is continuouslyregenerated.

WILLIAM A. BAILEY, JR.

